1. Field of the Invention
The present invention relates to a sheet feeding apparatus that performs sheet feed in such a manner as to separate sheets one by one from a bundle of sheets stacked in a sheet container and relates to an image forming apparatus including the sheet feeding apparatus.
2. Description of the Related Art
According to the related art, there are widely available sheet feeding apparatuses in image forming systems such as printers, copiers, and fax machines, the sheet feeding apparatuses feeding sheets in such a manner as to separate sheets one by one from a bundle of sheets stacked in a sheet container.
In addition, with the increase in user's needs in recent years, the demand has been increasing for feeding sheets of various sizes.
Japanese Patent Laid-Open No. 10-77123 proposes a sheet cassette that prevents occurrence of double feed, misfeeding, and the like in such a manner as to align leading edges, in the conveying direction, of sheets loaded in the sheet cassette with one another regardless of the size of the sheets and to keep constant a press-contact force applied to feed rollers. Specifically, the sheet cassette includes trailing-edge guides that align the trailing edges of the sheets in the sheet cassette and that have different heights so as to match respective different sheet sizes of stacked sheets.
In the sheet cassette described in Japanese Patent Laid-Open No. 10-77123, a user adjusts the position of each trailing-edge guide for aligning the trailing edges of the sheets; however, the position of the trailing-edge guide might not be adjusted properly.
A conceivable way of determining whether the trailing-edge guide is properly located is, for example, providing a trailing-edge detection member and a sensor for the trailing-edge guide. FIGS. 2A and 2B illustrate a specific configuration.
The sheet feeding apparatus in FIGS. 2A and 2B includes a vacuum separate/feed mechanism using air to suck and feed sheets. The sheet feeding apparatus also provides a system for determining whether the position of a trailing-edge guide is properly adjusted (hereinafter, referred to as trailing-edge rough-setting detection).
Details regarding the control of the trailing-edge rough-setting detection will be described later. In a case where trailing-edge rough-setting detection is performed, a trailing edge of a top sheet P that has not been fed completely might be up in the air while the leading edge of the top sheet P is held in a paper feed path, as illustrated in FIG. 3C. At this time, a sheet-surface detection sensor 525 incorrectly detects the top sheet P entering the paper feed path as a sheet located uppermost among sheets stacked as a sheet bundle 501. In reality, the sheet bundle 501 is located lower than the top sheet P, and thus a trailing-edge detection member 160 is not in contact with the sheet bundle 501. For this reason, in such a state as in FIG. 3C, the sheet feeding apparatus determines that a trailing-edge guide 504 has not been properly placed, even though the trailing-edge guide 504 has been properly placed against the sheet bundle 501.
As described above, in a case where a sheet feeding apparatus has both a vacuum separation mechanism and a system automatically performing the trailing-edge rough-setting detection, the sheet feeding apparatus might incorrectly detect the position of a trailing-edge guide in the determination of whether the position is properly adjusted.